1. Field of the Invention
The present invention relates to a method for resist pattern formation in which, in the formation of a resist pattern in a semiconductor or the like manufacturing process or the like, a covering layer is formed using a water soluble resin composition on a resist pattern and the covering layer in its part located near the resist pattern is crosslinked to form a modified covering layer which is insoluble in a developing solution on the surface of the resist pattern and covers the resist pattern, thereby effectively reducing the isolation size or hole opening size of the resist pattern to those below the limiting resolution. The present invention also relates to a water soluble resin composition suitable for covering layer formation.
2. Background Art
In extensive fields including the manufacture of semiconductors such as LSIs, the preparation of flat panel displays (FPDs) such as liquid crystal display (LCD) panels, and the manufacture of circuit boards for thermal heads and the like, photolithography has hitherto been used for the formation of fine elements or microfabrication. In the photolithography, a positive- or negative-working radiation-sensitive resin composition (photoresist) is used for resist pattern formation. The positive- or negative-working photoresist is coated onto a substrate, and mask alignment is conducted, followed by exposure and development to form a resist pattern. The resist pattern thus formed is utilized, for example, as an etching resist and a resist for impurity ion implantation in the manufacture of semiconductor devices, FPDs, and circuit boards, and as a plating resist or the like in the manufacture of magnetic heads or the like.
In recent years, increased integration density in semiconductor devices or the like has led to an ever-increasing demand for a reduction in wiring or element isolation width required of the manufacturing process. To cope with this demand, various attempts have been made, for example, to increase the fineness of the resist pattern using shorter-wavelength light, to form a finer resist pattern using a phase shift reticle or the like, and to develop a novel resist and a novel process that can meet the demand. In the conventional photolithography utilizing exposure, however, difficulties are encountered in the formation of a resist pattern which is finer than a limit determined by the wavelength of light for exposure. On the other hand, apparatuses for exposure of short wavelength light and apparatuses using a phase shift reticle or the like are disadvantageously expensive. To solve the above problems, a method for pattern formation has been proposed which comprises the steps of:
(1) providing a conventional positive- or negative-working photoresist and forming a pattern by a conventional method for pattern formation,
(2) providing an acid-crosslinkable covering layer on the formed resist pattern,
(3) heating the covered resist pattern to diffuse an acid from the resist pattern to crosslink the covering layer in its part located near the resist pattern to form a modified covering layer insoluble in a developing solution on the surface of the resist pattern, and
(4) conducting development to remove the covering layer in its part remaining uncured
to cover the surface of the resist pattern with the covering layer having a given thickness, whereby the resist pattern width or the opening size in a line-and-space (L/S) pattern is reduced to effectively form a resist pattern which is finer than a resolution limit determined by the wavelength of light for exposure (see, for example, Japanese Patent Laid-Open Nos. 241348/1993, 250379/1994, 73927/1998, and 19860/2001). This method has drawn attention as an effective method, because the size of the space part in the resist pattern can be effectively reduced without large investment of equipment such as an exposure system for short wavelengths.
The present inventors have made an application (Japanese Patent Application No. 45599/2003) directed to a water soluble resin composition, a method for resist pattern formation using the same, and a method for testing a resist pattern. This water soluble resin composition comprises poly(vinyl pyrrolidone-co-vinyl acetate) or poly(vinyl pyrrolidone-co-vinylimidazole) as a water soluble resin, p-toluenesulfonic acid triethylamine salt as an acid generating agent, and acetylenic alcohol as a surfactant. A covering layer having a satisfactory thickness can be formed with a high dimension accuracy on a highly water repellent resist pattern formed of, for example, a radiation-sensitive resin composition capable of coping with an ArF exposure, whereby the resist pattern can be thickened to effectively reduce the pattern size to such a level that renders the resist pattern finer than the limiting resolution and, at the same time, a change in measured value upon electron beam irradiation in measuring SEM can be prevented.
The above conventional method in which a resist pattern is covered with a covering layer to reduce the width between resist patterns in an L/S pattern or reduce the opening size of contact patterns and thus to effectively form a resist pattern which is finer than the limiting resolution determined by wavelength of light for exposure has mainly be intended for a resist pattern formed of a KrF resist (a radiation-sensitive resin composition capable of coping with KrF) and has been effective for the KrF resist. On the other hand, an ArF excimer laser exposure process has recently been proposed for finer resist pattern formation, and this has led to a proposal of an ArF resist (a radiation-sensitive resin composition capable of coping with ArF exposure). Transparency to a 248 nm light source has been required of the conventional KrF resist. On the other hand, the ArF resist should be transparent to a 193 nm light source. This inevitably leads to predominant use of a polymer having a structure comprising a protective group introduced into an acrylic or methacrylic resin or the like. For example, a protective group having an alicyclic structure has been proposed as the protective group. Due to the nature of the structure, the hydrophobicity of the polymer per se is higher than that of the KrF resist. On the other hand, the composition for a covering layer is in many cases a composition composed mainly of a water soluble resin and water from the viewpoint of preventing dissolution of the resist film as the first layer. For this reason, in many cases, the conventional water soluble resin composition for a covering layer has no satisfactory coatability on a highly water repellent resist pattern such as the above ArF resist. This has sometimes made impossible to form a good covering layer or modified covering layer. Further, in some cases, the level of fineness of the resist pattern layer has been unsatisfactory, probably because the diffusion of an acid from the resist pattern is unsatisfactory. Furthermore, in the prior art technique, an increase in complexity of the resist pattern has raised a problem of a difference in size reduction level in a coarse-and-fine pattern of the resist pattern. In Japanese Patent Application No. 45599/2003, it was found that the effective size of a resist pattern formed of a radiation-sensitive resin composition capable of coping with ArF can be reduced to a value beyond the liming resolution. However, there is a demand for an improvement in pattern size reduction effect, that is, the formation of a thicker modified covering layer.